FCC units used to conduct FCC operations commonly include a circulating inventory of bulk catalyst. The bulk catalyst is typically used to perform a primary function, such as producing naptha from petroleum feedstock, the naptha being further processed into gasoline. Additives, which are often in the same fluidizable and particulated form as the catalyst, are often introduced into the circulating inventory of bulk catalyst to perform a secondary function such as reducing certain types of emissions, e.g., SOx or NOx, produced by the FCC unit. These emissions are produced in the catalyst regenerator of the FCC unit where coke deposits from the cracked petroleum are burned off and the regenerated catalyst returned to the circulating catalyst inventory. These additives are usually introduced into the regenerator using an injection device commonly referred to as a “loader.” Loaders are also used to add catalyst to the bulk inventory as additional catalyst becomes necessary due to factors such as attrition and deactivation.
Particulate substances, such as catalysts and additives used in FCC units, are usually shipped from the manufacturer to the point of use, e.g., a refinery, in containers. For example, catalysts and additives are commonly transported in standard 55-gallon drums capable of holding approximately 300 pounds of the catalyst or additive. Tote bins capable of holding approximately 2,000 pounds of catalyst or additive are another type of commonly-used shipping container.
The containers used to ship catalyst or additive are usually covered during shipping to prevent contamination of the catalyst or additive by oxygen or moisture from the ambient environment. Covering the containers is also necessary to prevent fugitive emissions and other losses of the catalyst or additive, and to reduce the potential for human contact with the potentially toxic or caustic catalyst or additive.
The catalyst or additive can be unloaded from the shipping container to a silo or other suitable storage vessel at the refinery. The unloading process is typically conducted by removing the cover of the container, and vacuuming the catalyst or additive. Removing the cover is necessary to prevent a substantial pressure differential from developing between the interior of the container and the ambient environment. A substantial pressure differential can potentially collapse or otherwise damage the container.
Vacuuming the catalyst or additive while the cover of the container is removed, however, exposes the catalyst or additive to the environment. Such exposure can be disadvantageous in applications where the contents of the container are subject to contamination when exposed to the ambient environment. For example, many catalysts and additives degrade when exposed to moisture. Exposure to moisture can be particularly disadvantageous when the catalyst or additive possesses hygroscopic, i.e., moisture absorbing, properties.
Moreover, particulate substances that possess pyrophoric, i.e., spark or flame inducing, properties can present a fire or explosion hazard when exposed to or released into the ambient environment. Also, some types of catalysts and additives can degrade when exposed to the oxygen normally present in the ambient environment.
Consequently, an ongoing need exists for systems and methods that can facilitate the unloading of particulate substances from containers while minimizing or substantially eliminating exposure of the particulate substances to the ambient environment.